单选题：The Dangers of Secondhand Smoke　　Most people know that cigar

The Dangers of Secondhand Smoke
　　Most people know that cigarette smoking is harmful to their health. Scientific research shows that it causes many kinds of diseases. In fact, many people who smoke　get lung cancer. However, Edward Gilson has lung cancer, and he has never smoked　cigarettes. He lives with his wife, Evelyn, who has smoked about a pack of cigarettes a　day throughout their marriage.＿＿＿＿＿(46)
No one knows for sure why Mr. Gilson has lung cancer. Nevertheless, doctors
believe that secondhand smoke may cause lung cancer in people who do not smoke
because nonsmokers often breathe in the smoke from other people's cigarettes.
＿＿＿＿＿(47) The US Environmental Protection Agency reports that about 53,000
people die in the United States each year as a result of exposure to secondhand smoke.
　　The smoke that comes from a lit cigarette contains many different poisonous
chemicals. In the past, scientists did not think that these chemicals could harm a　nonsmoker's health.＿＿＿＿(48) They discovered that even nonsmokers had
unhealthy amounts of these toxic (有毒的) chemicals in their bodies. As a matter of fact,　almost all of us breathe tobacco smoke at times, whether we realize it or not. For　example, we cannot avoid secondhand smoke in restaurants, hotels and other public　places. Even though many public places have nonsmoking areas, smoke flows in from　the areas where smoking is permitted.
It is even harder for children to avoid secondhand smoke.＿＿＿＿(49)
　　Research shows that children who are exposed to secondhand smoke are sick more　often than children who live in homes where no one smokes and that the children of　smokers are more than twice as likely to develop lung cancer when they are adults as　are children of nonsmokers. The risk is even higher for children who live in homes where　both parents smoke.
　　People are becoming very aware of the dangers of secondhand smoke.＿＿＿＿(5O)
A．Recently, though, scientists changed their opinion after they studied a large group of "nonsmokers.
B．The Gilsons have been married for 35 years.
C．This smoke is called secondhand smoke.
D．However, secondhand smoke is dangerous to all people, old or young.
E．As a result, they have passed laws which prohibit people from smoking in many　public places.
F．In the United States, nine million children under the age of five live in homes with at　least one smoker.
请选择（46）处的最佳答案．